In the manufacturing process of semiconductor devices, associated with miniaturization of semiconductor devices, the demand of miniaturization has increased for photolithography technique. As a part of realizing miniaturization with photolithography technique, replacement is already being made in the exposure method of lithography, from exposure using conventional ArF excimer laser light having a wavelength of 193 nm to exposure using light in the EUV (Extreme Ultra Violet) range with a wavelength of 13.5 nm.
Since most substances have high light absorption property with respect to light in the EUV range, a hitherto known transmission type mask cannot be used as a mask for EUV exposure, and a reflection type mask is used as a mask for EUV exposure (EUV mask) (e.g., cf. Patent Literature 1). Patent Literature 1 discloses a technology of forming a light reflection film consisting of a multilayer film by alternately laminating molybdenum (Mo) layers and silicon (Si) layers on a glass substrate, and forming thereon a pattern with a light absorption body whose main component is tantalum (Ta).
In addition, since a dioptric system that utilizes transmission of light cannot be used for EUV light as described above, the optical system of an exposure machine will be a reflection type. Therefore, deflection utilizing a transmissive beam splitter is not possible. Thus, the reflective mask has a disadvantage of being unable to design incident light to the mask and reflected light therefrom to be on the same axis. Therefore, in an EUV mask, a technique is adopted in which reflected light of light, which had entered the mask and whose optical axis is tilted by about 6 degrees, is guided to a semiconductor substrate. In this technique, since the optical axis is tilted, a problem referred to as projection effect occurs in which the line width of the wiring pattern of a mask on a semiconductor substrate becomes different from that of a mask pattern, depending on the light incident direction with respect to the mask pattern. Therefore, for the purpose of suppressing or lessening the projection effect, it has been proposed to reduce the film thickness of an absorption film forming the mask pattern.
With the technique of reducing thickness of a light absorption film, since light attenuation amount that is required for absorbing EUV light becomes insufficient, light reflected to the semiconductor substrate increases, and a problem of sensitizing a resist film applied on the semiconductor substrate occurs. In addition, since exposure occurs on multiple faces on a chip on the semiconductor substrate, multiple exposures occur at boundary areas of adjacent chips. Furthermore, an EUV light source has a radiation spectrum having a peak at 13.5 nm, but is also known to radiate light other than that in the 13.5 nm band referred to as Out of Band, from vacuum ultraviolet ray to near-infrared light range. Since Out of Band is fundamentally unnecessary and sensitizes resist applied on the semiconductor substrate, Out of Band is unnecessary light that should be removed with a filter or the like.
However, a light absorption film using tantalum (Ta) also reflects light in a range from vacuum ultraviolet ray to deep ultra violet and near-infrared light range. Therefore, as described above, an unignorable amount of light accumulates on a semiconductor wiring part in the vicinity of the boundary area of adjacent chips, and causes a problem of affecting the dimension of the wiring pattern.
Proposed in response to this problem is a mask structure including a light-shielding frame (light-shielding band) where a surface quartz which is a base material is exposed by stripping, after stripping an absorption layer forming a pattern, a multilayer reflective film that contributes in reflecting EUV light to reduce reflected light at a chip boundary through means such as etching (cf. Patent Literature 2). However, Out of Band light has a problem of passing through quartz which is the base material, being reflected at a reverse-surface conductive film such as chromium nitride (CrN) formed on a surface opposite of the pattern side of the EUV mask, passing through the quartz again to be radiated to the semiconductor substrate side, and sensitizing the resist applied on the semiconductor substrate.